High transconductance cathoderay tube



Jan. 2, 1962 J. c. FRANCKEN HIGH TRANSCONDUCTANCE cATHoDE-RAY TUBE FiledJune ll, 1959 INVENTOR JAN CAR EL FRANCKEN AGENT Unite StatesY dde3,015,749 HIGH SCONDUCTANCE CATHODE- RAY TUBE Jan Carel Frauchen,Eindhoven, Netherlands, assignor to North American Philips Company,Inc., New York, N.Y., a corporation of Delaware Filed .lune 11, 1959,Ser. No. 819,659 Claims priority, application Netherlands lluly 17, 19585 Claims. (Cl. 315-3) The present invention relates to devicescomprising a cathode-ray tube, the gun of which at least comprises acathode, a control electrode and a first anode, and in which stepshavebeen taken for increasing the modulation curve slope or transconductanceof the gun.

It is known that the slope of the modulation curve of the gun of acathode-ray tube can be increased by applying the control voltages notonly to the control electrode but also to the first anode.

This can be effected in a simple manner by applying the control voltagesto the cathode since in this case the cathode potential alternates bothwith regard to the control electrode and with regard to the first anode.This effect is increased if the first anode has a considerablepenetration eect (durchgrif) on the cathode current, since an increasein voltage on the first anode then involves an appreciable increase ofthe electron current and consequently contributes to the increase incurrent produced by the control electrode.

In practice, however, it is found that limits are set to the increase ofthe penetration coefiicient of the first anode; As a matter of fact,this penetration coeicient may be increased by reducing the thickness ofthe control electrode and by diminishing the distance of the controlelectrode from the first anode and the cathode relatively to the openingof the control electrode. However, a limit is setto reducing theelectrode spacings on account of structural difficulties, while agreater grid-opening involves a larger picture spot on the screen andconsequently results in lower definition of the picture.

It is known to reduce these difculties by supplying an amplified signalto the first anode, the control signal being amplified by an amplifiertube which is in most cases arranged outside the cathode-ray tube. Thishas a limitation in that the higher capacity of the circuit elements andtheir lead-through and junction conductors to the anode and the grid ofthe amplifier tube adversely affects the bandwidth of the signal byincreasing the R-C time of these electrodes and the anode couplingresistance, since the required anode current of the amplifier tubeshould be heavy and the anode coupling resistance should be low, forexample 2000 ohms, in order for the R-C time to be maintained sucientlyshort with the higher capacity.

These disadvantages are accentuated if the electrodes of the gun arelocated very close together in order to increase the penetrationcoefficient of the first anode, since the capacity is also increasedthereby. Hence, the amplifier tube has to carry a considerable heavycurrent (approximately 20 to 30 ma. anode current).

If the triode system is incorporated in the gun of a cathode-ray tube, aconsiderable increase of the R-C time will still occur because withknown circuits, a number of circuit elements is present, whichpreferably should also be incorporated in the cathode-ray tube if theincrease in capacities of the auxiliary amplifier is to be maintainedlow relative to earth which, in turn, involves difficulties inconjunction with the liberation of gas of these component parts, unlessusing expensive particular parts. Moreover, such component parts occupymuch room, which is a serious limitation since the usual dimensions ofthe neck of the cathode-ray tube scarcely allow of introducing the gun.

In a device comprising a cathode-ray tube of this type, in which anamplification system is incorporated in the gun, said disadvantages areavoided for the major part, if in accordance with the invention, thecontrol grid of the amplification system is directly electricallyconnected to the cathode of the gun, and the anode of the amplificationsystem is directly electrically connected to the first anode of the gun,while the control range of the control grid of the amplification systemat maximum anode voltage (white picture) exceeds one-third of thecontrol range of the gun at a minimum voltage of the first anode (blackpicture). The term control range is here to be understood to mean therange of they control electrode voltage between the cut-off point andthe point at which the control electrode itself will collect current.The invention yields the advantage that, as the case may be, only theanode-coupling resistor of the amplification system need be housed inthe neck of the cathode-ray tube and that this resistor may have acomparatively high value, since the capacities relative to earth can bemaintained low. As -a result, the amplification system has to carry onlya small current (approximately 4 ma. or less). Also, it is no longernecessary highly to increase the penetration coefficient'of the firstanode artificially, and the control electrode and the first anode can bespaced more widely from each other, thus reducing the capacity betweenthese electrodes. By suitably shaping the control electrode of the gunand the first anode, this capacity may attain an extremely low value.Consequently, this permits the gun to be built as advantageously aspossible with a View to the desired size of the picture spot.

In a specific example, the cathode for the triode-section has a diameterof 1.8 mm. and a length of the emitting surface of 6 mms, The gridconsists of turns of 60 micron wires, wound with a pitch of 0.4 mm. Thecathode-grid spacing is 300 microns, and the grid to anode spacing is350 microns. The distance between the gun cathode surface and thecontrol electrode is microns, and the distance between control electrodeand first anode is 250 microns.

In order that the invention may be readily carried into effect, anexample will now be described in detail with reference to theaccompanying drawing, in which FIG. l is -a sectional view of lacathode-ray tube having a gun with incorporated amplification system,and

FIG. 2 shows schematically the circuit arrangement of a gun comprisingan amplifier according to the invention.

In the drawing, the reference numeral 1 designates the cathode forproducing the electron beam. The cathode 1 is secured to a ceramic tube,2 containing a heating member 3. A cathode 4 with an electron-emissivelayer 5 is provided on the lower part of the ceramic tube 2, whichcathode is surrounded by a grid 6 and an anode 7. The grid 6 has such `aconsiderable pitch (400 microns) and is so located relatively to thecathode 4 and the anode 7 that the control range of the triode exceedsone-third of that the gun at the Voltage value of the first anode at theinstant the picture is blackf In front of the cathode 1, provision ismade of a control electrode 8 for controlling the intensity of theelectron beam, a first accelerating anode 9 and final anode 10. The-aggregate is incorporated in a glass envelope 12 of a cathode-ray tube.As shown schematically in FIG. 2, the cathode 1 of the gun is directlyconnected to the grid 6 of the triode system, while the first anode 9 isdirectly connected to the anode 7 of the triode and, through a resistor11, to a source of direct voltage of +220 v. The grid 6 and the cathode1 are connected to the anode of the video-output tube 13 and areconnected, through a resistor 14, to a positive voltage of, say, 9() v.The cathode 4 of the triode is connected to a supply of +75 v. As may beseen, solely the resistor 11 need be incorporated in the vacuum space,in contrast to the aforesaid conventional arrays. This resistor may have`a comparatively high value (for example 30,000 ohms), while the gun maybe proportioned as advantageously as possible in the usual manner inview of the picture to be reproduced.

Hence, no undue compromise need be made for an additional increase inpenetration coefficient from the first anode to the cathode. A suitablevalue of the penetration coe'icient is, for example, 40 to 50%.

As a result of the shape of the control electrode 8 and the first anode9 their relative capacity is very low, the more so since their relativespacing need not be minimal. As a matter of fact, this may then be 250microns. As a result, the R-C time of the anodes 7, 9 and the resistor11 despite the use of a resistor 11 having a comparatively high value,may be suciently low to maintain an adequate bandwidth. In thisembodiment, the capacity is lower than the permissible maximum capacityof, say, 2 pf.

Since the construction of the triode is substantially independent ofthat of the gun itself, the pitch and size of the grid and of the anodemay be chosen -to be such that if the anode voltage is maximum (forexample 150 v.), that is with a white signal, a large control range(approximately to 30 v.) is obtained. This control range should exceedone-third of and may even be equal to that of the control electrode ofthe gun, which latter control range amounts to approximately V. at aminimum first anode voltage (with black signal approximately 60 v.).

When the picture is black, no gun current flows, which means that, withcathode injection of the video signal, the cathode is most positive andso is the control grid 6 of the amplifying triode to which it isdirectly connected. With the grid 6 most positive, maximum tube-currentflows, which means that the plate 7, and the gun anode 9 to which it isdirectly connected, are at their minimum voltage value.

Although only one embodiment has been described, it will be evident thatthe structural design of the gun and of the triode system may, withinthe scope of the invention, be varied.

What is claimed is:

1. A cathode-ray tube comprising an envelope, an electron beam producingelectrode system within the envelope and comprising a first cathode, afirst control grid, and a first accelerating anode, an amplifyingelectrode system also within the envelope and comprising a secondcathode, a second control grid, and a second anode, an

impedance within the envelope, means directly connecting the first andsecond anodes together and to said impedance, means for applying to theimpedance a potential, means directly connecting together the firstcathode and the second control grid, and means for applying a signalpotential to the connected first cathode and second control grid.

2. A tube as set forth in claim 1 wherein the impedance is a resistor, acommon heating filament is provided for the first and second cathodes,the beam producing electrode system has a planar geometry, and theamplitying electrode system has a cylindrical geometry.

3. A cathode-ray device comprising an envelope, an electron beamproducing electrode system within the envelope and comprising a firstcathode, a first control grid, and a first accelerating anode, anamplifying electrode system also within the envelope and comprising asecond cathode, a second control grid, and a second anode, an impedance,means directly connecting together the first and second anodes andcoupling said direct connection to said impedance, means for applying tothe directly connected anodes through the impedance a potential, wherebythe voltages appearing directly at the anode electrodes vary betweenminimum and maximum values as a function of the current flow through theamplifying electrode system, and means directly connecting together therst cathode and the second control grid, said amplifying electrodesystem having a control grid voltage range, between that value ofcontrol grid voltage at which current through the electrode system iscut-off and that value at which current flows to the control grid, atthe maximum second anode voltage greater than one-third of thecorresponding control grid voltage range of the beam producing electrodesystem at the minimum first anode voltage.

4. A device as set forth in claim 3 wherein means are provided forcoupling a signal voltage to the directlycoupled first cathode andsecond control grid.

5. A device as set forth in claim 3 wherein the impedance is a resistorhaving a high value of resistance, and the second control grid comprisesa winding having a large pitch.

References Cited in the file of this patent UNITED STATES PATENTS2,163,210 Wienecke June 20, 1939 2,173,498 Schlesinger Sept. 19, 1939FOREIGN PATENTS 1,089,337 France Sept. 29, 1954

